Silverside roast beef HELP I AM A RUBBISH COOK

[lavender11]

OK, i expect no one is going to look at this tonight
I have a silverside roast beef and a beef and ale sauce suitable for beef (M&S) and a slow cooker
If I proposed to take the silverside roast beef (has net string round it and a small layer of fat but not too much fat) out of the freezer (i.e it is 10.30pm) and put it with the sauce in a slow cooker to defrost and "marinade" overnight) with a view to turning slow cooker on tomorrow morning 7.30am) to eat at 8.30pm - what are the pitfalls
I am assuming that because I have not properly defrosted there will be a horrible layer of fat in the slow cooker? What else? Sorry if all of you proper cooks are laughing but any assistance greatly appreciated
thanks

it is not safe to cook partially frozen food in a slow cooker as it doesn't cook at a high enough temperature.

If the beef is not fully defrosted you need to fully defrost it in the microwave before putting it in the slow cooker.

If the beef is cooking in the sauce all day there is no need to marinade it.

what if i put it in the slow cooker now (i.e 11pm) frozen (it is not a big joint) and put the low heat on it tomorrow morning at 7am with a view to eating it tomorrow (8.30pm) - ie 10 hour defrost 13 hours plus low cooking
will it be dried out beyond belief?? (the lid of the slow cooker will be on)